Re: 1988 60hp mercury cooling
Yes that motor should have a thermostat and popit valve on the head just left of the top spark plug. The water tell tail should start flowing usally within 30 seconds or so as the motor cooling areas get full of water. If the tell tail dose not start fairly quickly it might be pluged. A piece of weedeater string run in the tell tail will clear most blockages. If it still dose not pump water you could need a new impeller or compleat rebuild kit depending on how the cup and plate look. I try to replace impellers at least every 3 years. JMO
Oldman570